1. Field of the Invention
The present invention relates to a semiconductor light-emitting device which includes a plurality of semiconductor laser elements formed on the same substrate and is mounted on a package using solder, and a manufacturing method thereof, and more particularly, to a semiconductor light-emitting device and a manufacturing method thereof capable of preventing polarized light of each semiconductor laser element from rotating before and after mounting on the package.
2. Background Art
As a recording speed multiplication factor increases, light output required for a recording type high-output laser diode is increasing in an accelerating pace. Furthermore, it is important to obtain a stable light beam polarization characteristics so as to efficiently input the light output to an optical system. When the polarization characteristics is not stable, the efficiency of injecting light into the optical system declines, requiring a greater amount of light output.
Since solder is used to mount a semiconductor laser element on a package, the temperature at the time of mounting needs to be set to as high as 300° C. or more. Therefore, residual stress remains at an operating temperature of 100° C. or below due to a difference in the linear expansion coefficient between the semiconductor laser element and the package.
FIG. 15 is a perspective view showing a conventional semiconductor light-emitting device with one semiconductor laser element formed on a substrate (e.g., see Japanese Patent Laid-Open No. 2002-246333). One semiconductor laser element 10 is formed on a GaAs substrate 11. Furthermore, Au plating 16 is formed on the principal surface of the semiconductor laser element 10. Solder 18 is applied to the Au plating 16 and a plurality of semiconductor laser elements 10 are mounted on a submount 19 using this solder 18. The submount 19 is mounted on a package 22 using solder 21.
Here, the linear expansion coefficient of GaAs which is the material of the GaAs substrate 11 is 6(×10−6/° C.). On the other hand, the linear expansion coefficient of Fe often used as the material of the package 22 is 11. Furthermore, the linear expansion coefficient of Cu often used as the material of the high radiation package 22 is 17. Directly mounting the semiconductor laser element 10 on the Fe package 22 using the solder 18 may cause the semiconductor laser element 10 to be destroyed by residual stress produced due to a difference in the linear expansion coefficient. When the Cu package 22 is used, the difference in the linear expansion coefficient further increases and the residual stress also increases.
Therefore, to reduce the influence of this residual stress, the submount 19 made of AlN having a linear expansion coefficient of 4 is inserted between the package 22 and the semiconductor laser element 10. The linear expansion coefficient of the submount 19 is approximate to that of the GaAs substrate 11 and its mechanical intensity is also large, and therefore residual stress can be reduced. However, even this structure cannot reduce the residual stress to 0.
When only one semiconductor laser element 10 is formed on the GaAs substrate 11, the residual stress after assembly applies to the left and right sides of the light emitting area of the semiconductor laser element 10 symmetrically. Therefore, rotation of polarized light does not occur compared to before the assembly.